Method and device for continuous casting and extrusion

ABSTRACT

Apparatus consists of an articulated continuous casing machine (1) in which a mould for casting bar (18) moves endlessly from an upstream end to a downstream end of a path on the urging of an engine (15). To enable the cast bar to be fed directly into a continuous extrusion machine (2), the engine (15) engages the mould via a slipping clutch (15A) so that in operation an axial compressive force is applied to the cast bar in the mould.

The present invention concerns the provision of apparatus for and amethod of manufacturing extruded metallic products by casting andsubsequently extruding a bar of metal alloy. The alloy will commonly bealuminium and for the present purposes the term alloy should beunderstood to include the pure metal as well as mixtures with otherelements and compounds. It should be understood that alloys of othermetals such as copper or magnesium may also be processed in accordancewith the present invention.

It is frequently desirable to recycle scrap alloys. To achieve this itis commonly necessary to first cast the scrap into an elongate bar readyfor subsequent processing. An articulated continuous casting machinesuitable for this purpose is disclosed in GB-1305964. This continuouscasting machine has two mould sub-assemblies each of which consists of atrain of mould elements supported by an endless track and engaged with adrive means to be continuously displaced around the track. Each trackhas an elongate mould section co-extensive with and opposite the mouldsection of the other sub-assembly. As the mould elements are moved intothis section, the mould element in front is engaged and a correspondingmould element of the other, overlying, subassembly is engaged. Thus, anelongate, closed mould is assembled and moves continuously from anupstream end of the mould section to the downstream end. At thedownstream end each mould element separates from the following mouldelement and is returned to the upstream end. In use molten alloy iscontinuously injected into the upstream end of the mould, the speed ofwhich is controlled to ensure the solidification of the alloy by thetime it reaches the downstream end. Thus a bar of cast alloy can becontinuously separated from the mould and either coiled or cut intolengths for subsequent storage and transport before further processing.

While it is sometimes desirable to coil and store the bar for laterprocessing, it is also at times desirable to simultaneously cast andfurther process the bar by extrusion.

Continuous extrusion is commonly carried out in a continuous extrusionmachine such as that disclosed in Lamitref's patent applicationGB-2095592. Such continuous extrusion machines have a wheel, rotatablymounted in a support structure. An endless groove is formed in theperiphery of the wheel and an abutment, mounted adjacent an extrusiondie intrudes into the groove. In use, alloy bar is entrained in thegroove and drawn around until it engages the abutment. Subsequentlyfriction heats the bar in the groove until the alloy is sufficientlymalleable to extrude through the die. In Lamitref's patent applicationthe bar is formed by casting in a wheel and belt caster and fed directlyto the continuous extrusion machine.

The apparatus proposed by Lamitref is not useful when it is desired toproduce bar stock for storage preparatory to subsequent extrusionprocessing and consequently lacks versatility. Conversely, it has provendifficult to feed continuously cast bar from the articulated typecontinuous casting machine to a continuous extrusion machine because ofthe problems encountered in coordinating the speeds of the castingmachine and extrusion machine. This is a difficult problem because thecast bar formed in the casting machine tends to be cracked andsusceptible to breakage when subject to stress. It would however by verydesirable to enable direct continuous extrusion from bar castcontinuously in an articulated casting machine to enhance plantversatility.

Accordingly the present invention seeks to provide apparatus forcontinuously casting and extruding alloy comprising a continuous castingmachine having a mould movable along an endless path, and a continuousextrusion machine arranged downstream of the casting machinecharacterised in that the mould of the continuous casting machine is ofarticulated type and the mould is driven by means including a slippingclutch whereby a compressive axial force can be applied to a cast barfed directly from the casting machine to the extrusion machine.

Further according to the present Invention there is provided a method ofcontinuously casting and extruding alloy comprising the steps of:continuously feeding molten alloy into the upstream end of a movingmould in an articulated, continuous casting machine to cast a bar,feeding the cast bar directly from the continuous casting machine to acontinuous extrusion machine and controlling the speeds of the machinesso that a compressive axial force is applied to the cast bar to preventthe bar from cracking.

To achieve the method defined above the drive means of the castingmachine of the apparatus according to the invention is powered at alevel which would move the mould at a speed exceeding the rate at whichthe cast bar is ingested by the extrusion machine. Consequently the castbar is pushed in an upstream direction and slips, relatively upstream inthe mould, thereby compensating for the shrinkage of the cast barrelative to the mould and preventing the cast bar from cracking.

Preferably the slipping clutch is of friction type. However,electromagnetic or hydraulic coupling devices may also be useful for thepresent purposes.

It is preferable to control the speed of the continuous extrusionmachine (that is to sat the wheel speed) in accordance with thedimensions of the cast bar sensed by a sensor device, so that thedimensions of the cast bar are maintained substantially constant. Thisis found to be more convenient than varying the rate of introduction ofmolten alloy to the mould.

In known continuous casting machines of the articulated type, two trainsof moulds are required to assemble the mould. This leads to a complexmachine into which it is difficult to introduce molten alloy, especiallywhere it is desired to cast bar of small section (that is having asection of less than 25×25 mm).

Consequently an aspect of the present invention provides a castingmachine of articulated type having not more than a single train of mouldelements supported to be moved around an endless path to form anendlessly movable elongate mould. In this case the mould comprises anelongate channel which is open at the top at least the upstream end atleast. Thus molten alloy can readily be poured into the mould. Byproviding for an open topped channel mould, it is possible to easilyintroduce molten alloy into a mould having dimensions to cast a bar ofless than 25×25 mm square section or similar sectional area. Furthermoreit is advantageous in that the cast bar is readily accessible throughthe open top for the purpose of sensing the thickness and hence thecross section of the bar as far upstream as possible. Thus, the singletrain continuous casting machine is particularly well adapted to theapparatus and method of the invention.

In the conventional articulated continuous casting machine the elementsof the mould are displaced at one speed while the elements travellingalong the path from the downstream end to the upstream end are driven ata different speed. This demands a complex drive mechanism. In apreferred form of the articulated casting machine according to thepresent invention, each mould element engages the leading and followingmould elements. Thus when one mould element is displaced, all of theelements in the train are displaced at the same speed making speedcontrol much simpler. The conventional continuous casting machinerequires the mould elements to be supported by an endless track.However, the casting machine according to a preferred constructionembodying the present invention has each mould element linked to themould element in front of it by means of an articulated joint. Thus themould elements form an endless articulated belt which can convenientlybe supported by two horizontally spaced pulleys and the mould supportedby several rollers. The belt may thus be advantageously driven via oneof the pulleys engaged with a motor via the slipping clutch.

An example of apparatus and a method embodying the present inventionwill now be described, with reference to the accompanying drawings inwhich:

FIG. 1 is a diagrammatic side view of the apparatus,

FIG. 2 is a view on the line II--II of a mould element of the apparatus,

FIGS. 3a and 3b are enlarged views of the mould elements supported onpulleys,

Referring to the figures, the apparatus comprises an articulated castingmachine 1, a continuous extrusion machine 2 and a control unit `C`.

The continuous casting machine 1 has an endless articulated belt 3Aformed from many mould elements 3. The belt 3A is entrained around twohorizontally spaced pulleys 4, 5 mounted for rotation about horizontallydisposed axis 4A, 5A. Thus the belt 3A can be displaced around anendless path. The path includes an uppermost mould section defined bythe part of the belt 3A extending between the upper peripheries of thepulleys 4, 5; and a cooling section consisting of the part of the belt3A extending between the lower peripheries of the pulleys 4 and 5.

Each mould element 3 comprises an elongate block with a channel 9extending longitudinally in it and opening into the outermost surface ofthe mould element 3. The innermost edges 10 of the ends of each mouldelement are connected by pivots 10A to the adjacent edge 10 of theadjacent mould element to articulately join the elements 3 into thearticulated belt 3A. The end faces 11 of each mould element 3 areadapted to co-operate with the adjacent end face 11 of each adjacentmould element when the elements are traversing the mould section 6 ofthe path, to form a leak proof junction.

In operation, the pulleys 4, 5 rotate in a clockwise direction so thatthe portion of the belt extending along the mould section 6 moves in adownstream direction from the pulley 4 to the pulley 5. As each mouldelement 3 moves into the upstream end of the mould section it cooperateswith the preceding mould element to form a mould. The mould is supportedby freely rotatable rollers 8 to prevent sagging.

The cooling section 7 of the path passes through a bath 12 of coolantwater 13.

An alloy feeding station is provided by a chute 14 which is arranged tofeed molten alloy into the upstream end of the open topped mould duringuse.

A motor 15 engages the pulley 5 by means of a drive chain 16 and aslipping clutch 15A so that operation of the engine 15 rotates thepulley 5 and propels the belt 3A around the endless path. It should beappreciated that the drive arrangement shown, may be varied by drivingthe pulley via a gear train or drive shaft. The slipping clutch may be asimple friction clutch, an electromagnetic clutch or an hydraulicclutch.

In some embodiments of the apparatus (not shown) a single engine can bearranged to drive both the casting machine and the extrusion machine,via suitably geared drive trains.

In the preferred embodiment the pulleys 4, 5 are circular and haveradially extending flanges 5B. The pins of the articulated jointsproject laterally from the mould elements to ride on the rims of theflanges. To improve driving engagement between the pulley 5 and the belt3A the flanges may be notched.

In an alternative embodiment of the apparatus the pulleys 4, 5 may bepolygonally shaped so that flat faces of the pulleys 4, 5 engage theundersides of the mould elements.

In use the belt is displaced by operation of the engine 15 so that themould moves endlessly downstream. Once the mould is in motion moltenalloy 17 is introduced into the mould by the chute 14 at a constantrate. As the alloy is carried towards the downstream end of the mould itcools into a cast bar 18 which is then separated from the mould at thedownstream end. It will be appreciated that by cooling the mouldelements 3 in the birth 12 the rate of cooling the molten alloy 17 isincreased thereby enabling the mould to be made of short length. Coolingis further enhanced by spraying coolant from sprays 22 onto the mouldelements of the mould.

As the cast bar 18 is separated from the mould it is guided by rolls 20into the continuous extrusion machine 2. The continuous extrusionmachine has a wheel 21 with an endless groove (not shown) formed in it.The wheel is rotationally driven by a motor (not shown) so that thealloy bar 18, which is entrained in the groove is drawn into theextrusion machine 2, heated and pressurised by frictional engagementwith the groove and forced through an extrusion die in known fashion.

During the continuous casting and extrusion process the speed of thecasting machine motor 15 and the speed of the wheel 21 are sensed andcontrolled so that the slipping clutch 15A is constantly slippingbecause the casting machine motor 15 is trying to propel the mould andcast bar 18 at a speed exceeding the feed rate of the continuousextrusion machine 2. Thus a compressive axial force as applied to thecast bar 18. This has the effect of preventing cracking and compensatingfor shrinkage of the cast bar, hence alleviating the risk of the castbar breaking.

The speed of the casting machine motor can thus be set and maintainedconstant without complex controls.

To control the thickness of the cast bar 18, the speed of the wheel 21is controlled by an electronic control unit C in accordance with thethickness of the bar detected by a sensor 19. If the sensor 19 detectsan increase in the bar thickness beyond a predetermined range value thespeed of the wheel 21 is increased. This allows the cast bar to movemore quickly thereby increasing the speed of the mould and hencereducing the thickness of the bar towards an acceptable range value.Conversely, if the thickness of the bar detected by the sensor 19decreases below a predetermined lower range value, the speed of thewheel 21 is reduced so that the cast bar moves at a slower speed therebyreducing the speed of the mould and returning the bar thickness to anacceptable range value. Thus the bar thickness can be maintainedconstant without the disadvantageous problem of varying the feed rate ofmolten alloy to the mould.

It will be appreciated from this that the simple feature of including aslipping clutch in the drive to the casting machine and driving thecasting machine motor 15 so that an axial force is always applied to thecast bar as it separates from the mould provides a simple and reliableway of preventing the bar breaking.

It will readily be recognised that the articulated continuous castingmachine can also be operated to cast bar for subsequent coiling andstorage. In this case it is still advantageous to apply the compressiveaxial force to prevent the bar breaking. Other advantages of the castingmachine, such as the relatively simple construction will also beapparent.

We claim:
 1. Apparatus for continuously casting and extruding metalcomprising a continuous casting machine (1) having a mould movable alongan endless path, and a continuous extrusion machine (2) arrangeddownstream of the casting machine (1) the continuous casting machine (1)having an articulated mould driven by a drive around the endless pathvia a slipping clutch (15A) whereby the drive can be arranged to apply acompressive force to a cast bar (18) fed directly from the castingmachine to the continuous extrusion machine (2), the compressive forcebeing governed by the slipping clutch (15A), a bar thickness sensor(19), a control unit (C) being means for controlling the rate at whichthe continuous extrusion machine ingests the cast bar in response to thebar thickness measured by the sensor, so that the speed of thecontinuous casting machine (1) is governed by the speed of thecontinuous extrusion machine whereby the bar thickness can be maintainedconstant.
 2. Apparatus according to claim 1 wherein the casting machine(1) comprises not more than one endless path.
 3. Apparatus according toclaim 2 wherein the mould is formed from a plurality of mould elements(3A) and each mould element (3A) engages the mould element in front ofit at all times.
 4. Apparatus according to claim 3 wherein the mouldelements (3A) engage by means of a joint articulated by a pivot (10A) toform an endless belt.
 5. Apparatus according to claim 4 wherein theendless belt is supported by two horizontally spaced pulleys (4, 5)mounted for rotation about horizontal axes.
 6. Apparatus according toclaim 5 wherein a casting machine motor (15) engages one of the pulleys(5) to provide the drive means to propel the belt around the endlesspath.
 7. Apparatus according to claim 5 wherein the lower part of thebelt is immersed in a coolant bath (12).
 8. Apparatus according to claim5 wherein the upper part of the belt spanning between the pulleys (4, 5)forms the mould, and spray means (22) is disposed to cool the mould. 9.Apparatus according to claim 1 wherein the mould is open topped topermit easy introduction of the alloy.
 10. Apparatus according to claim9 to wherein the mould comprises a casting channel to cast a bar with across section of not more than 625 mm².
 11. A method for continuouslycasting and extruding metal comprising the steps of:continuously feedingmolten metal into the upstream end of a moving articulated mould in acontinuous casting machine to cast a bar, feeding the cast bar directlyfrom the continuous casting machine to a continuous extrusion machine,operating at least one engine to drive the continuous casting machineand the continuous extrusion machine, applying a compressive axial forceto the cast bar characterised in that the drive to the continuouscasting machine includes a slipping clutch to govern the compressiveforce, and controlling the rate at which the continuous extrusionmachine ingests the cast bar by a control unit responsive to thethickness of the bar being cast, whereby the speed of the castingmachine is controlled by the speed of the continuous extrusion machineso that the bar thickness and feed rate of molten metal can bemaintained constant.